Apparatus for screening sand and gravel mixtures



6 1942- J. H. WHITEHEAD ETAL 2,269,046

G SAND AND GRAVEL MIXTURES APPARATUS FOR SCREENIN Filed July 12, 1938 ATTORNEY.

Patented Jan. 6, 1942 APPARATUS ron SCREENING SAND AND GRAVEL MIXTURES v James H. Whitehead, Westfield, N. J., and Christian Mathiesen, Albany, N, Y., assignors to Whitehead Brothers Company, 'Jersey City, N. J a corporation of New Jersey Application July 12, 1938, Serial No. 218,726

1 Claim. 101109-284) This invention relates'more especially to the screening of mixtures of sand and gravel in order to effect the separation of so-called fines, namely the sand and accompanying fine clay particles from the gravel, roots and other relatively large aggregates.

The principal objects of the invention are-the provision of means for maintaining a protective or buffer sifting layer of the fines, for example sand and accompanying clay on a predetermined area of the separator screen to thereby more effectively accomplish the sorting of the gravel from the fines while at the same time expediting the sifting operation. Other objects of the invention are the provision of a compact, eco-v nomical and highly eflicient apparatus suitable for accomplishing such purpose. 1

In the accompanying drawing in which we have illustrated a preferred form of sand screening apparatus for carrying out our improved method of separating sand and gravel mixtures,

Figure 1 is a diagrammatic .vertical section;

partly in elevation of such apparatus whereina conveyor belt, having an associated adjustable.

scraper, is mountedprincipally within the main are supported on and adapted to be rotated by rollers 3. Said rollers are fixed on a longitudinal shaft 4 that is mounted in bearing blocks 5 which in turn are supported on H-beams 6, all in the Well known manner. An electric motor 1 serves to drive the shaft 4 and thereby effects rotation of the rollers 3 and the screen i at the desired optimum speed of rotation.

As shown, said rotary screen is so mounted that its longitudinal axis inclines downwardly toward a discharge hopper 8, the outlet of which is controlled by a sliding door or gate 9, all in the well known manner. A chute Ill, having downwardly converging sides, is mounted immediately below the screen, the width of the chute at its top being substantially the same as the diameter of the screen and the width at its bottom being slightly less than that of a travelling delivery conveyor belt H, which latter is reeved over terminal rollers l2 that are rotatably mountis provided with wheels M which travel on tracks l5 and, as shown, said belt is adapted to be ad- .justed longitudinally so as to admit of the material received by the belt being discharged into cars positioned at different distances from the supporting frame Work of the screen. Within the rotating screen is also mounted a secondtravelling belt IS, the same being reeved over terminal rollers [1, which latter are mounted on av channel iron frame l8 that is longitudinally mounted on the uprights of the supporting frame work. Guide rollers [9 are mounted at intervals on said frame I8, the same serving to support said belt and prevent the sagging thereof. A delivery hopper serves .to discharge the natural sand and gravel deposit which is obtained from the sand banks orthe'like onto said belt l6, said mixture being supplied to the, hopper by means of an escalator belt 2| of the well known type.

Intermediate the ends of thebelt IS, the side members'of the frame 18 are provided with a series of tapped holes 22 for the reception of cap bolts 23, by which opposing brackets 24, 24' are bolted to said frame. A scraper or doctor blade 25'is'bolted to the respective brackets 24, 24'; and as shown, saidbrackets are located at different positions longitudinally of said frame in order that said scraper will extend obliquely across the longitudinal axis of said belt, preferably at an angle of about Thebelt I6 is adapted to be revolved by means of an electric motor'265 When employing the apparatus illustrated in Figs. v1 and 2'for screening anatural sand deposit from a riverbankwhichusually contains substantial amounts of gravel, in the form of pebbles of varying size, as well as roots and other debris of relatively large size as compared with the sand and clay particles, the mixture is carried up the escalator belt 2| from which it is discharged from the hopper 20 onto'the conveyor belt 16. As the mixture reaches the obliquely disposed scraper 25-, the same will be discharged onto the inner surface of the screen I and will form a protective buffer layer a along the bottom of the screen that willbe of maximum dimension ed on a channel iron frame l3. The latter frame 5 at the point immediately. below the scraper and the meshes thereof (these meshes are usually such as to afford a free opening whose dimensions are about /4" x A"), while the gravel and other debris will be prevented from passing through the mesh of the screen by such buffer layer of the mixture and will gravitate along said layer until they reach the end thereof and thence pass into the hopper 8. The separated sand and clay particles associated therewith will pass into the chute H) and be discharged therefrom onto the delivery belt H from which the same are discharged to a freight car or other vehicle.

The position of the scraper 25 will depend upon the dryness of the mixed sand and gravel and the clay content thereof for example, the sand and clay particles in an extremely dry mixture tend to quickly filter through the screen I and consequently in order to maintain a bufier layerof the mixed material on the inner bottom area of the screen, the scraper should be disposed at that point, where after the discharge of the mixture from the belt [6, a continuous buffer layer of the mixture of gradually diminishing depth will remain on the screen, as indicated by the reference letter a, almost to the extreme lower end thereof, whereby substantially no gravel, roots and other large debris will sift through the screen but will pass out through the open end thereof into the hopper 8 while on the other 'hand substantially all of the sand and smaller particles in the mixture will sift through the screen onto the conveyor belt II and practically none of the same will be lost due to the escape thereof into the gravel hopper 8. In those cases where the sand and gravel mixture is extremely wet and .especially when there is also substantial clayey bond in the mixture, the scraper can be located at or near the end of the belt it which is nearest the high end of the screen I, while still insuring the maintenance of the desired buffer layer and thereby the maximum sifting capacity of the screen can be realized.

Through the employment of our novel means of screening sand and gravel mixtures it is possible to at all times realize the maximum efliciency from the screening apparatus and also to maintain the rate of feed of the material to the screen at all times, at :an optimum rate commensurate with the character of the mixture being screened whereas in the ordinary screening apparatus if the screen is of sumcient capacity for handling mixtures which are wet and heavily bonded, such screen is oversize' for the screening of relatively dry mixtures and consequently it is customary to compromise on the size of size.

screen employed by providing a screen whose capacity is below the maximum required for wet and heavily bonded material and yet is of excessive capacity for extremely dry material with the resultant material sacrifice of efiiciency of operation.

The sand particles in the sand and gravel mixture range from a maximum size which will pass through a six mesh to the lineal inch screen to particles of '75 mesh or even finer size, whereas the pebbles and other debris will range from a size larger than the sand, but capable of passing through the aforesaid screen wherein the free openings are of A" square to a much larger However, by the maintenance of the buffer layer sand upon such screen, such pebbles and other larger debris particles will be substantially entirely prevented from passing through the portion of the screen covered by such bufier layer, notwithstanding the fact that were the screen bare, many of said pebbles and other particles would be sufficiently small to pass through the screen. Furthermore the maintenance of said buffer layer tends to materially prolong the life of the screen since it prevents excessive erosion thereof by the pebbles which are to a large extent prevented from directly contacting the screen at least for any prolonged period of time.

Various modifications and changes within the scope of the appended claim may be made without departing from the spirit of our invention as embraced therein.

Having thus described our invention, what we claim and desire to obtain by United States Letters Patent is:

In an apparatus for screening sand to remove gravel and debris therefrom, the combination comprising a longitudinally inclined cylindrical screen of a mesh considerably coarser than the sand and also coarser than a substantial part of the gravel to be separated from such sand, means for rotating said screen, means for delivering a mixed charge of sand and gravel onto the bottom inner surface of said screen at a point intermediate the ends thereof, said means including a rotatably mounted conveyor belt and an adjustable scraper blade extending across the same at an oblique angle and whose edge is in close proximity thereto and means for adjusting said scraper,

. a separate conveyor belt positioned below said 

